1. Field of the Invention
This invention pertains to methods for detecting the presence, location, and concentration of moisture in roof coverings.
2. Description of the Prior Art
Large industrial and commercial buildings often have flat roofs which require a covering for protection from the elements. This covering often consists of multiple layers of tarpaper or felt which are bonded together, usually by covering each layer with hot tar or bitumen before emplacement of another layer. A layer of heat insulating material is commonly provided between the structural roof and the multiple felt layers.
Over a period of time, natural weathering forces result in a deterioration of the integrity of the roof covering. Alternate heating and cooling of the roof causes cracks to appear in the tarpaper or felt. Moisture seeps between the layers and expands by freezing during the winter and evaporation during the summer, with consequent further separation and cracking of the layers. Eventually the covering deteriorates to the point that water leaks into the insulation and through the roof, necessitating replacement of the damaged portion of the covering.
For purposes of convenience in illustration, the deterioration of multiple layer roofs in wet areas may be classified as first stage penetration, second stage penetration, and extensive water penetration or third stage penetration. First stage penetration is the initial phase of water penetration into the roof. The top layers of felt may be somewhat porous from asphalt and tar breakdown from normal weathering, or water may be found between two layers arriving by capillary action from a surface imperfection. There are no leaks into the building at this stage of deterioration, but roof damage may continue at a rapid rate unless the situation is corrected and water entry points sealed. Second stage penetration is similar to first stage penetration except that deterioration has progressed into the lower layers of roofing felts. Water may now be sandwiched between three or four felt layers instead of just the top two as in first stage penetration. While there still may be no water leakage into the building at the second stage, the protective layers of the roof are in very bad shape and leakage into the building can be expected at any time. The felt-bitumen layers must be replaced. The insulation layer in most cases can be salvaged, but should be inspected to determine its condition. At the third or extensive water penetration stage, water has penetrated all the protective felt layers and the insulation as well. Since the binders used in most insulation are water soluble, the roof water often dissolves the binders, and the insulation deteriorates and becomes mushy and also looses its heat insulation ability. In this third stage of extensive water penetration, both the felt layers and the underlying insulation are soaked, and the entire roof covering must be removed and rebuilt from the structural roof on up using new materials.
In general, first stage penetration areas can be most easily repaired by top-coating with a cold applied roofing mastic or an elastomeric coating material. If the penetration is indicated as coming from a flashing crack or tear, the repair should be made with an elastomeric material applied over a polyethylene mesh tape. Asbestos filled bitumastic materials work for temporary repairs. These are not satisfactory for long-term repairs because they become brittle and cracked to again allow water entry.
Second stage penetration indicates much more severe roof deterioration. Only temporary repairs can be made with the top layers. Permanent corrective repairs for second stage penetration areas requires the removal of existing felt plys down to the insulation to completely remove all trapped water. Where visual inspection indicates excessive deterioration of the insulation, it should be removed. The roof should be rebuilt from the insulation on up, or as required from the decking on up, using standard roofing techniques and new dry materials. Hot tar and hot asphalt felt laminates are satisfactory here because all roof water has been removed. Hot roofing materials do not work well over areas in a roof containing moisture, and therefore should not be used in these areas. The repair areas are built up to the level of the existing older built up roofing, and properly overlapped. Cold process roof mastics or elastomeric coatings are applied as a final protective top coat.
Generally, roof covering does not deteriorate over an entire roof at once, and repair or replacement of the entire covering is not justified. However, it may be difficult to define the areas of the covering that need repair or replacement, since water may travel a considerable distance between the layers to the point where the leak in the roof appears. The traditional method of determining areas of wetness in roof coverings has been to take core samples of the covering. This method is time consuming and has the obvious disadvantage of risking destruction of sound roof covering if too great an area is tested, while deteriorated covering far from the point of leakage may be missed if extensive samples are not taken. Moreover, core sampling is an impractical method for detecting the first stages of roof deterioration, which as noted above can often be repaired without replacement of the covering.
Several non-destructive roof wetness testing techniques have been developed in an attempt to reduce the time and expense of testing roofs. These techniques include infrared scanning of roofs to detect cool moist areas, and nuclear particle bombardment to determine hydrogen ion count in the roof covering. Such techniques generally require expensive and delicate equipment, and do not discriminate the first stage and second stage penetration wet areas from dry areas with as high a degree of accuracy as is desirable.